Functional magnetic resonance imaging (fMRI) is a type of MRI scan that measures the change of blood flow related to neural activity in the brain. fMRI relies on a blood oxygen level dependent signal. Blood flow to local vasculature that accompanies neural activity results in a local reduction in deoxyhemoglobin, which is paramagnetic. Thus, fMRI is one type of MRI that facilitates mapping brain activity.
fMRI has conventionally been performed using an echo planar imaging (EPI) Cartesian based approach. fMRI has conventionally suffered from limited coverage, limited speed, and spatial distortions in the image acquired in the limited coverage area. These undesirable effects are related, at least in part, to the fact that the center of k-space is only crossed once during a Cartesian acquisition and that there is only one effective time per TR (repetition time) in EPI.
These undesirable effects may be exacerbated when under-sampling occurs. Example aliasing artifacts associated with conventional Cartesian EPI fMRI are illustrated in FIG. 1. A fully-sampled sixty four line Cartesian acquisition 110 produces an image 120 with a point spread function 130. An under-sampled sixteen line Cartesian acquisition 140 produces an image 150 with a point spread function (PSF) 160. Note the aliasing artifacts in image 150.